Question is, would you rather have an hour in your prime, or 2.5 hours in retirement.
That's how it works, right?
Myself, I'm not overweight - I weigh about 60kg, and am 1.75m tall - but I don't exercise. I don't see that it's worth the amount of time it takes out of my day.
My perspective may change if I find myself physically challenged in anything I do. But that seems to be some way off just yet.